In producing objective materials from wafers, metals, plastics, and so on, it is general to operate processing procedures such as cutting and grooving works. For instance, after completing a semiconductor chip fabrication process, a process for cutting a wafer to separate plural chips, which are formed on the wafer, into individual chips is subsequent thereto. The wafer cutout operation is very important over the whole process of semiconductor chips because it heavily affects the productivity and product quality in the subsequent process. The wafer cutout operation is usually carried out with a mechanical cutout method or a method employing a laser beam.
In a mechanical processing apparatus such as a sawing device, after mounting a wafer on a stage, a cutting blade of the sawing device contacts to a cutting position (i.e., street), with rotating in a predetermined speed, and then severs (or cuts out) the wafer into unit chips. During this, the sludge generated by the wafer cutting operation is removed therefrom by ejecting a cleaner thereto. However, when a wafer is severed by means of the mechanical processing method, it is impossible to completely remove the sludge by a cleaner and inevitable to be operable with a wider cutout breath. Especially, when it needs to sever a wafer in a relatively smaller size, the wider cutout breath may cause damages on circuits formed in the wafer. Even with a way to overcome the problem by adjusting an edge width of the blade, there is a limit to narrow the edge width of the blade.
Recently, it has been studied a technique of processing a wafer in the manner of non-contactable form with a laser beam. In order to conduct a wafer by means of a laser beam, after settling a substrate support, on which a wafer is mounted, on a transfer unit, a laser beam emitted from a light source is transmitted through a condensing lens and then irradiated on the wafer.
The processing method with a laser beam uses a mechanism of burning irradiated areas out of the wafer due to inducing effects of heating and chemistry by focusing the laser beam on a surface of the wafer in the range of ultraviolet rays 250˜360 nm. In other words, when a laser beam is condensed and irradiated on a wafer, the irradiated area is heat up instantly and then evaporated, as well as being melted, to increase a vaporizing pressure according to the evaporation of the wafer material, resulting in an explosive burning-out of the irradiated area. From a successive sequence of the burning-out operations, a wafer can be divided into multiple chips and a linear or curved severing process is available therein.
However, even in the processing method with a laser beam, it is also impossible to clearly remove the sludge therefrom such as in the mechanical sawing method. Further, it has disadvantages that the sludgy particles vaporized or evaporated by the irradiation of a laser beam are condensed and recasted on sidewalls of a wafer, without being discharged outside, as a recess depth of a processing plane.
Moreover, the laser processing method currently used is workable with transferring an object only or a laser beam irradiator. This is inefficient to carry out a mass-production process such as a multi-pass cutting operation, and needs to assure the stability of a transfer unit to move an object in a high speed, which causes an apparatus heavier and a product cost higher.